Wireless communication in multi-rat system

ABSTRACT

A buffer status reporting scheme for a terminal ( 10 ) wishing to transmit data simultaneously in multiple RATs of a wireless communication network, which enables the co-ordination of multiple base stations ( 12, 14 ) of different RATs (e.g. LTE eNB, UMTS base station, WiFi access point, etc.) with the assistance of the terminal ( 10 ) in order to achieve efficient radio resource scheduling for multi-RAT multi-flow aggregation in uplink. A radio bearer is configured for multi-RAT multi-flow aggregation by the network, and multiple logical channel IDs are assigned to this RB that may be associated with different RATs. Logical channels associated with a certain RAT (or a given set of RATs) may be grouped into one logical channel group for radio resource scheduling reason. The terminal ( 10 ) performs buffer status reporting, according to the configuration, on all involved RATs and sends reports/indications to one or more involved base stations ( 12.14 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of InternationalApplication PCT/EP2013/071775, filed on Oct. 17, 2013 and claims thebenefit of European Application No. 12189345.7, filed Oct. 19, 2012, inthe European Intellectual Property Office, the disclosure of which isincorporated herein by reference.

FIELD OF THE INVENTION

This invention generally relates to a wireless communication system and,in particular, to a method of transmitting data from a terminalsimultaneously using multiple radio access technologies to one or morebase stations/access points.

BACKGROUND OF THE INVENTION

Wireless communication systems are widely known in which a terminal,subscriber station or user equipment (henceforth referred to as a UE forconvenience) communicates wirelessly with a base station (or accesspoint) by use of a certain radio access technology (RAT). Examples ofsuch a RAT include the 3GPP family of standards including GSM, GPRS,UMTS and LTE, as well as WiMAX (IEEE802.16), CDMA and WiFi (IEEE802.11).

Although conventionally, a UE employs only one RAT at a time for itscommunication, UEs such as smartphones are increasingly capable ofsupporting more than one RAT simultaneously and moreover, several radioaccess networks (RANs) employing various RATs may be available in thesame place, offering the possibility of multi-RAT communication toincrease the overall bandwidth available to the UE. Since each RATavailable in a given area may have its own base station, this impliesthat the UE is able to send or receive data to and from multiple basestations employing multiple RATs (and thus via multiple cells, in thecase of cellular systems such as 3GPP or WiMAX) simultaneously.

Henceforth, for convenience, the term “RAT” is also used to denote awireless communication system employing a specific RAT. Thus, “multi-RATcommunication” means communication via a plurality of wirelesscommunication systems which involve the use of a plurality of differentRATs. The term “network” is used henceforth to denote the totality ofall such wireless communication systems within a given geographicalarea, except as demanded otherwise by the context.

Similar technologies where the base stations belong to the same RAT(Radio Access Technology), such as Carrier Aggregation (CA) orCooperative Multi-point operation (CoMP), have been introduced into 3GPPsince LTE release 10. In CA two or more Component Carriers (CCs) atdifferent frequencies are aggregated in order to support widertransmission bandwidths up to 100 MHz. A UE may simultaneously receiveor transmit on one or multiple CCs depending on its capabilities. InCoMP the cooperating base stations operate at the same carrierfrequency. Details of CA and CoMP as applied to LTE are given in the3GPP standard TS36.300.

Where the base stations support different RATs the co-operation becomesmore difficult. Before discussing the problems involved, it may behelpful to outline the protocol layers involved in a wirelesscommunication system, taking LTE as an example.

As is well known, current wireless communication systems are constructedby dividing the tasks to be performed among a plurality of layeredprotocols, each node or entity in the system being equipped to processdata at various layers (or levels within a layer) in a protocol stack,with the protocols at corresponding layers notionally communicating witheach other. Although ultimately all signalling in the system is carriedby the lowest, physical layer, this hierarchical arrangement allows eachlayer to be considered independently.

FIG. 1 shows a protocol stack in each of three main types of nodes in anLTE-based wireless communication system. These nodes are the UE 10(subscriber station such as a mobile handset), an eNodeB 12 (the basestation in an LTE system, also called eNB), and a Mobility ManagementEntity or MME 16 (a higher-level node for controlling mobility of UEs,in other words handovers between eNodeBs, and for setting up “bearers”as discussed below). As shown in FIG. 1, apart from non-access stratum(NAS) protocols, all the protocols terminate in the eNodeB 12 on thenetwork side.

The horizontal bands in the Figure represent individual protocols withinthe protocol stack of each node in the system, and each protocol is partof a particular protocol layer within the well-known OSI model. Withrespect to a given node, each protocol can be considered to reside in afunctional module or “entity” which can be considered separately fromprotocols in other layers. This allows, among other things, for the useof the concept of “radio bearers”, which provide a kind of tunnelbetween peer entities in the base station and UE at a given protocollevel for user data or control signalling. Radio bearers are associatedwith “logical channels” which link SAPs (Service Access Points) forpeer-to-peer communication between MAC and RLC protocol layers discussedbelow.

Packets belonging to the same radio bearer get the same end-to-endtreatment in the network. There are two main bearer types, GuaranteedBit Rate (GBR) and non-GBR. For GBR bearers, the network guarantees acertain bit rate to be available for the bearer at any time. Thebearers, both GBR and non-GBR are further characterized by a Maximum BitRate (MBR), which limits the maximum rate that the network will providefor the given bearer. In this way it is possible for each radio bearerto provide a certain quality of service, QoS. For each radio bearer,which exists between the UE 10 and the eNodeB 12, there is acorresponding access bearer between the eNodeB and a Packet Data NetworkGateway, PDN GW (not shown).

FIG. 2 is a slightly less conceptual view than FIG. 1, showing theprotocol stack for one node and concentrating on the uplink (that is,the direction of transmission from the UE to the network). FIG. 2illustrates how packets are exchanged between protocols at differentlayers, and shows the effect of Radio Resource Control, RRC on managingvarious protocols. The protocol stack in FIG. 2 is for handling usertraffic (such as data being uploaded) and is referred to as the “userplane”, as distinct from the “control plane” used to carry networksignalling.

As indicated in FIGS. 1 and 2, there is a physical layer protocol PHY atthe lowest level, Layer 1, responsible for actual wireless transmissionof data over the air, using the frequency band(s) of the RAT in use, andemploying the transmission scheme of that RAT; for example, in the caseof the downlink in LTE, this is orthogonal frequency divisionmultiplexing (OFDM). In LTE, the unit of data transfer in the PHY is theTransport Block (TB). The TBs are passed to the PHY layer from thenext-higher layer (MAC) once per Transmission Time Interval (TTI) of 1ms. Scheduling can be performed in units of 1 TTI or more, in otherwords on a timescale as short as 1 ms.

Thus, in the case of the uplink, packets are processed insuccessively-lower levels in the protocol stack before being passed tothe PHY for conversion to radio signals for transmission to the network.Incidentally, within each protocol the packets are referred to as“protocol data units” (PDUs) and the PDUs of one level in the stack formso-called Service Data Units (SDUs) of the next stage, possibly afterconcatenation or segmentation. Each TB from the PHY corresponds to a MACPDU.

Above the PHY there are the layer-2 protocols MAC, RLC and PDCP.

MAC stands for Media Access Control and is responsible for managing theso-called hybrid ARQ function (see below), and for extracting differentlogical channels out of the transport block for the higher layers.Format selection and measurements provide information about the networkthat is needed for managing the entire network.

Logical channels exist at the top of the MAC. They represent datatransfer services offered by the MAC and are defined by what type ofinformation they carry. Types of logical channels include controlchannels (for control plane data) and traffic channels (for user planedata). Transport channels DL-SCH and UL-SCH are in the transport blocksat the bottom of the MAC. They represent data transfer services offeredby the PHY and are defined by how the information is carried, differentphysical layer modulations and the way they are encoded.

A MAC entity of the eNB in an LTE system includes a scheduling functionresponsible for managing resource scheduling for both uplink anddownlink channels, that is, to allocate physical layer resources for theDL-SCH and UL-SCH transport channels. Different schedulers operate forthe DL-SCH and UL-SCH. The scheduler should take account of the trafficvolume (buffer status) and the QoS requirements of each UE andassociated radio bearers, when sharing resources between UEs. Schedulersmay assign resources taking account the radio conditions at the UEidentified through measurements made at the eNB and/or reported by theUE. Radio resource allocations can be valid for one or multiple TTIs.

Likewise, the terminal (UE) has a MAC entity with a scheduling functionfor, in accordance with a resource allocation signalled to it by theeNB, constructing transport blocks from data for transmission which hasarrived in a buffer of the UE.

The Hybrid Automatic Repeat-reQuest (HARQ) process, done in combinationbetween the MAC and the PHY, allows retransmission of transport blocksfor error recovery.

The retransmission is performed by the PHY, and the MAC performs themanagement and signalling. The MAC indicates a NACK when there is anerror in a cyclic redundancy code, CRC, added to a transport block, andthe PHY usually indicates that failure. Retransmission is done by theeNodeB or the sender on the downlink using a different type of coding.The coding is sent and maintained in buffers in the eNodeB. Eventually,after one or two attempts, there will be enough data to reconstruct thetransport blocks.

The MAC layer receives RLC PDUs from the next-higher layer-2 protocol,RLC. RLC stands for Radio Link Control, and performs segmentation andreassembly and operates in three modes: transparent mode (TM),acknowledged mode (AM) and unacknowledged mode (UM). These are used bydifferent radio bearers for different purposes. The RLC providesin-sequence delivery and duplicate detection.

Other wireless communication systems such as UMTS and WiMAX also employRLC. Although WiFi (IEEE802.11) does not employ a RLC protocol as such,the logical link control (LLC) layer in WiFi has a similar role.

The next protocol in the stack above RLC, still within layer-2 of theOSI model, is PDCP. PDCP stands for Packet Data Control Protocol and,being of particular interest for present purposes, is described in somedetail. Further details can be found in 3GPP standard TS 36.323.

ROHC referred to below stands for Robust Header Compression and refersto a technique used to reduce the header size of packets in LTE. SinceLTE is completely IP-based, voice calls have to be carried using IP(Voice over IP or VoIP) and without some measure to reduce the headersize, this would be inefficient.

PDCP functions in the user plane include decryption, ROHC headerdecompression, sequence numbering and duplicate removal. PDCP functionsin the control plane include decryption, integrity protection, sequencenumbering and duplicate removal. There is one PDCP entity (in otherwords, PDCP instance) per radio bearer. Therefore, different PDCPentities exist which are associated with either the control plane or theuser plane depending on the type of bearer.

FIG. 3, taken from the above mentioned TS36.323, is a functional view ofthe PDCP layer. In this Figure, u-plane denotes the user plane andc-plane, the control plane. The left-hand portion of the Figure showfunctional blocks involved on the uplink and the right-hand side showsthe functions performed on the downlink.

As shown in FIG. 3, the PDCP layer is responsible for various tasksincluding:

-   -   Sequence numbering, which allows in-order delivery of packets,        and duplicate detection: if the PDCP layer receives packets with        the same sequence number, then it discards duplicates and does        not send them to upper layers    -   Header compression and decompression for user plane data    -   Integrity protection and verification for control plane data        (however, there is no integrity protection offered to the user        plane data)    -   Ciphering and Deciphering of user plane and control plane data    -   Addition/removal of a PDCP Header    -   (not shown) Security and Handover functions.

There is one to one correspondence between a PDCP SDU and a PDCP PDU.That is, there is no segmentation or concatenation in the PDCP layer.Addition of a PDCP header, applying compression and security on the PDCPSDU makes a PDCP PDU. Similarly deciphering, decompression and removalof the PDCP header makes a PDCP SDU from a PDCP PDU.

In LTE, the above mentioned radio bearers (RBs) are defined at variousprotocol levels including PDCP. There are two kinds of PDCP bearers: SRB(Signalling Radio Bearer) and DRB (Dedicated Radio Bearer). There areonly two SRBs—SRB1 and SRB2. These are used by control plane protocol tosend the packets to the UE. DRBs are used for sending voice and data; asmany DRBs are set up as the number of QoS streams or services requiredby the terminal. When a DRB is set up, a Logical Channel Identity (LCID)will be assigned to this DRB for UL and DL. In this sense, it may besaid that one logical channel (LC) conventionally corresponds to one RB.For the purpose of resource allocation, the logical channels may in turnbe assigned to Logical Channel Groups (LCGs). Conventionally, a givenLCID or LCG can be associated with only one RAT.

Layer 3 protocols in the UE include RRC or Radio Resource Control, whichis responsible for connection management, bearer control, and handoversto other base stations, UE measurement reporting, and QoS management.

Finally NAS stands for Non-Access Stratum which forms the highest-levelof communication between the UE 10 and MME 16. The layers under the NASare also referred to as the Access Stratum (AS) since they concern theradio access network which terminates at the eNodeB. NAS protocolssupport the mobility of the UE and the session management procedures toestablish and maintain IP connectivity between the UE and a packet datanetwork gateway, PDN GW. They define the rules for a mapping betweenparameters during inter-system mobility with 3G networks or non-3GPPaccess networks.

Returning now to the scenario of CA within LTE, the typical Layer 2structures for downlink and uplink with CA configured in LTE networksare illustrated in FIGS. 4 and 5 respectively. As is apparent from theseFigures, the multi-carrier nature of the physical layer is only exposedto the MAC layer for which one HARQ entity is required per serving cell.In both uplink and downlink, there is one independent hybrid-ARQ entityper serving cell and one transport block is generated per TTI perserving cell in the absence of spatial multiplexing. Each transportblock and its potential HARQ retransmissions are mapped to a singleserving cell.

When CA is configured, the UE only has one RRC connection with thenetwork. At RRC connection establishment/re-establishment/handover, oneserving cell provides the NAS mobility information (e.g. Tracking AreaIdentity, TAI), and at RRC connection re-establishment/handover, oneserving cell provides the security input. This cell is referred to asthe Primary Cell (PCell). Generally, one carrier corresponds to onecell. In the downlink, the carrier corresponding to the PCell is theDownlink Primary Component Carrier (DL PCC) while in the uplink it isthe Uplink Primary Component Carrier (UL PCC).

However, the above discussion relates to a single RAT (namely, LTE). Theproblem addressed by this invention is in a wireless communicationsystem where multiple radio access technologies (e.g. GSM, UMTS, LTE andbeyond, WiMAX, WiFi, etc.) are available in the whole network or incertain areas, such as city centres (either full time, or during peakhours only).

For simplicity, LTE and WiFi will be used as an example of multiple RATsco-existing in a wireless communication system. FIGS. 6(A) and 6(B)illustrate two examples of typical deployment scenarios in such system;in case (A), the LTE eNB and WiFi AP are separated (in other wordsprovided by different pieces of equipment), while in case (B) the LTEeNB and WiFi AP are co-located, in other words a single unit acts as acombined LTE base station and WiFi access point. In both cases, the UEsare assumed to be dual (or more) mode devices having a WiFi interface.It is further assumed that there is some form of backhaul network (suchas broadband Internet) connecting both the eNB and AP to a core network.

Based on the current 3GPP standard as set out in TS36.300, measurementreports, including transport volume and measurements of a UE's radioenvironment, are required to enable the scheduler in the eNB to operatein both uplink and downlink. Especially, in the uplink direction, uplinkbuffer status reports (BSR) are needed from the UEs to provide supportfor QoS-aware packet scheduling by the eNB.

The uplink buffer status reports refer to the data, ready for uplinktransmission, that is buffered for a group of logical channel (LCG) inthe UE. Four LCGs and two formats are used for reporting in uplink:

-   -   A short format for which only one BSR (of one LCG) is reported;    -   A long format for which all four BSRs (of all four LCGs) are        reported.

Uplink buffer status reports are transmitted using MAC signalling. RRCcontrols BSR reporting by configuring the two timers periodicBSR-Timerand retxBSR-Timer and by, for each logical channel, optionallysignalling logicalChannelGroup which allocates the logical channel to anLCG.

The LC may be assigned to the RB, and LC may be assigned to a LCG, whenthe RB is set up; however it may be useful to reassign LCs to LCGs forexample when a new RB is added or an existing RB is removed. If anexplicit configuration is not signalled, there is a defaultconfiguration, but only for SRBs.

For RATs other than LTE, the concept of a LCG may not be explicitlydefined; nevertheless it is still possible to group radio bearerssharing common characteristics (QoS, bit rate, delay and so on). Theterm “logical channel group” includes such groupings.

Based on current 3GPP specifications, BSR can be used for intra-RAT(i.e. intra-LTE) cases only when CA or CoMP is configured. However, inthe multi-RAT scenarios (as shown in FIG. 6) resource scheduling betweenthe RATs becomes very challenging; especially for FIG. 6(A) where LTEeNB and WiFi AP are separated and backhaul support cannot be assumed tobe ideal for the information exchange between the multi-RAT nodes. Thekey issue in such scenarios in the uplink is how sufficient informationcan be provided via buffer status reports to assist the network toco-ordinate the radio resource scheduling with multiple nodes ofdifferent RATs in order to achieve efficient UL multi-flow aggregation.The present invention is mainly intended to address this issue.

US 2012/0140743 A1 discloses a method according to the preamble of claim1, wherein a terminal receives, over a primary channel associated with afirst RAT, provisioning information of a supplementary channelassociated with a second RAT.

WO 2011/088612 A1 discloses methods that provide for control signallingin multi-radio access environments. One method includes implementingradio resource management and a general link layer jointly across atleast two radio access technology modules, and selecting one of theradio access technology modules to perform control signalling in amulti-radio environment.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda method for uplink communication between a terminal and a multi-RATwireless communication network comprising one or more base stations, themethod comprising:

in the multi-RAT wireless communication network,

-   -   configuring radio bearers, each radio bearer to be carried by        one or more radio access technologies, RATs, among a plurality        of RATs available to the terminal, and    -   associating logical channels with radio bearers by assigning to        each radio bearer one or more logical channels; characterised by

in the terminal,

-   -   transmitting one or more buffer status reports wherein at least        one of the buffer status reports contains information on data to        be sent on a first set of logical channels associated with a        first set of said radio bearers where the first set of radio        bearers is to be carried by more than one RAT.

Here, RAT means radio access technology such as GSM, GPRS, UMTS and LTE,as well as WiMAX (IEEE802.16), CDMA and WiFi (IEEE802.11). Whererequired by the context, RAT means a wireless communication systememploying the RAT for its operation. Preferably, one of the RATs is LTE.

The multi-RAT wireless communication network, below referred to simplyas “network”, means the combined wireless communication systemsavailable to the terminal unless otherwise demanded by the context.

The terminal includes any kind of subscriber station, user equipment orother wireless device of a user, whether mobile or fixed, and can alsoextend to a relay station.

The base station includes any form of radio access node employed in agiven RAT for providing an air interface with wireless devices, andincludes for example an eNB of an LTE wireless communication system, ora base station of a UMTS wireless communication system, as well as anaccess point in a WiFi WLAN.

The radio bearer, apart from its specific meaning in the context of LTE,can be regarded as a service provided by the access stratum of a RAT tothe non access stratum (core network) for delivering data between aterminal and the core network.

In addition to the above mentioned configuring in the network, typicallysome configuration will also occur in the terminal.

The data to be sent, information on which is contained in the bufferstatus reports, refers to data in a buffer of the terminal, used to holddata temporarily prior to uplink transmission. In the present inventionat least one buffer status report contains information on data to besent and relating to more than one RAT, or more correctly defined, withrespect to a set of logical channels associated with a set of bearerscarried by more than one RAT. The buffer status reports may betransmitted for the purpose of assisting the multi-RAT uplinkscheduling.

A logical channel means some form of designation applied to radiobearers, for example for the purpose of scheduling. Variousrelationships are possible among the radio bearers (RBs), the RATs, andthe logical channels. For example, embodiments of the present inventioninclude the case of: (i) multiple RATs and multiple RBs, where one of aplurality of configured RBs is carried by only one RAT; and (ii) whereone or more RBs may each only be assigned one logical channel.

Preferably, one or more groups of logical channels are configured fromamong the first set of logical channels, and the at least one of thebuffer status reports contains information on data to be sent on each ofthe one or more groups of logical channels.

At least one of the one or more groups of logical channels may beconfigured to contain a second set of logical channels associated with asecond set of radio bearers where the second set of radio bearers is tobe carried by more than one RAT. Here, the second set is a subset of thefirst set.

Alternatively the method may further comprise configuring a second setof logical channels associated with a second set of radio bearers to becarried by a single RAT, the method further comprising the terminal,prior to transmitting buffer status reports, assigning data to the thirdset of logical channels for uplink transmission in accordance with atleast one of:

a preference for that single RAT;

a signal quality with respect to that single RAT;

a quality of service requirement for the data; and

a network constraint on usage of that single RAT.

A further, optional step of the method is the network, granting, inrespect of a said set of logical channels associated with a said set ofsaid radio bearers, uplink resources on one or more RATs on the basisof:

the one or more buffer status reports; and

a network policy on usage of each RAT for uplink data transmission.

Alternatively the above configuring may further comprise configuring asecond set of logical channels associated with a second set of saidradio bearers to be carried by one or more of the plurality of RATsavailable to the terminal excluding a specific RAT.

In one form of the method, the buffer status report is transmitted toeach base station providing one or more of the RATs to which the bufferstatus report relates. In other words the report may be received fromthe terminal separately by multiple base stations.

Alternatively the buffer status report is transmitted to a base stationoperating according to one or more of the RATs, which base stationforwards at least the relevant part of the buffer status report to oneor more base stations operating according to the or each other RAT bywhich the first set of radio bearers is configured to be carried. Inthis way, it is sufficient if only one of the base stations receives thereport from the terminal.

Preferably the buffer status report includes one or more entries foreach RAT covered by the report, in other words for each RAT by which thefirst set of radio bearers is configured to be carried, and the terminalindicates a preference not to employ a given RAT for its uplinktransmission by use of one or more reserved values, such as zero, in atleast one entry with respect to that RAT in the buffer status report.

Alternatively the buffer status report includes entries for only asubset of the RATs by which the first set of radio bearers is configuredto be carried, the terminal indicating a preference not to employ agiven RAT for its uplink transmission by omitting the entry for that RATfrom the buffer status report.

More generally, in the case of one or more entries in the buffer statusreport for each RAT, the terminal indicates a preference not to employ agiven RAT for its uplink transmission by omitting at least one of theone or more entries in the buffer status report which is or areassociated with the given RAT

According to a second aspect of the present invention, there is provideda multi-RAT wireless communication system comprising:

a terminal arranged to perform at least uplink communication via firstand second RATs;

first base station means for the first RAT; and

second base station means for the second RAT; wherein

the first and second base station means are arranged to co-operate toconfigure radio bearers to be carried at least on the uplink by one ormore of the first and second RATs, and to associate logical channelswith radio bearers by assigning one or more logical channels to theradio bearer; characterised in that

the terminal is arranged to assist said multi-RAT uplink scheduling bytransmitting one or more buffer status reports wherein at least one ofthe buffer status reports contains information on data to be sent on aset of logical channels associated with a set of said radio bearers tobe carried by more than one RAT.

According to a third aspect of the present invention, there is provideda base station using a first RAT for use in a multi-RAT wirelesscommunication system in which system a terminal is arranged to performat least uplink communication via first and second RATs; the basestation arranged to:

co-operate with a second base station which uses the second RAT, toconfigure radio bearers to be carried at least on the uplink by one ormore of the first and second RATs, and to associate logical channelswith radio bearers by assigning one or more logical channels to theradio bearer; characterised in that the base station is further arrangedto:

receive, from the terminal, one or more buffer status reports wherein atleast one of the buffer status reports contains information on data tobe sent on a set of logical channels associated with a set of said radiobearers to be carried by the first and second RATs; and

assign, in respect of the set of logical channels associated with theset of said radio bearers, resources for uplink transmission by theterminal in the first RAT, in co-operation with the second base stationassigning resources in the second RAT, on the basis of the at least oneof the buffer status reports.

Here, preferably, the base station is further arranged to forward to thesecond base station at least a portion of the buffer status reportrelating to the second RAT.

According to a fourth aspect of the present invention, there is provideda multi-RAT base station provided for wireless communication at least onan uplink with a terminal via first and second RATs and arranged to:

configure radio bearers, each of the radio bearers to be carried atleast on the uplink by one or more of the first and second RATs, andassociate logical channels with radio bearers by assigning one or morelogical channels to each radio bearer; characterised in that the basestation is further arranged to:

receive, from the terminal, one or more buffer status reports wherein atleast one of the buffer status reports contains information on data tobe sent on a set of logical channels associated with a set of said radiobearers to be carried by the first and second RATs; and

assign, in respect of the set of logical channels associated with theset of said radio bearers, resources in the first and second RATs foruplink transmission by the terminal on the basis of the at least one ofthe one or more buffer status reports.

According to a fifth aspect of the present invention, there is provideda terminal for use in a multi-RAT wireless communication system in whichthe terminal is arranged to perform at least uplink communication viafirst and second RATs; the terminal arranged to:

receive a configuration of radio bearers to be carried at least on theuplink by one or more of the first and second RATs, in whichconfiguration logical channels are associated with radio bearers byassigning one or more logical channels to each radio bearer;characterised in that the terminal is further arranged to:

transmit one or more buffer status reports wherein at least one of thebuffer status reports contains information on data to be sent on a setof logical channels associated with a set of said radio bearers wherethe set of radio bearers is to be carried by the first and second RATs;and

receive, in response to the buffer status reports, an assignment ofresources for uplink transmission by the terminal in the first andsecond RATs with respect to the set of logical channels.

In another aspect, the present invention relates to a computer program(which may be stored to a computer-readable medium) comprising programcode for causing a computer to carry out a method as described in thepresent application or to operate as a terminal as described in thepresent application or as a base station as described in the presentapplication.

Thus, the present invention enables a novel buffer status reportingscheme which enables the co-ordination of multiple base stations ofdifferent RATs (e.g. LTE eNB, UMTS base station, WiFi access point,etc.) with the assistance of the UEs in order to achieve efficient radioresource scheduling for multi-RAT multi-flow aggregation in uplink.

When the radio bearer RB (with multi-RAT multi-flow aggregationconfigured) is set up by the network, multiple logical channel IDs areassigned to this RB that may be associated with different RATs. Logicalchannels associated with a certain RAT (or a given set of RATs) may begrouped into one logical channel group for radio resource schedulingreason. On the terminal side, the UE performs the buffer statusreporting procedure, according to the configuration, on all involvedRATs and sends reports/indications to one or more involved basestations.

Working at the PDCP layer in accordance with the present inventionprovides more flexibility for multi-RAT aggregation, in comparison withother approaches such as providing aggregation at the MAC level.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present application are described, by wayof example, with reference to the accompanying drawings in which:—

FIG. 1 shows a protocol stack employed in a 3GPP wireless communicationsystem;

FIG. 2 illustrates an uplink flow of packets between the protocol layersin FIG. 1;

FIG. 3 shows the functions of a PDCP entity in the PDCP protocol layer;

FIG. 4 illustrates the Layer 2 structure for the downlink of a wirelesscommunication system configured for carrier aggregation (CA);

FIG. 5 illustrates the Layer 2 structure for the uplink of a wirelesscommunication system configured for carrier aggregation (CA);

FIGS. 6(A) and (B) show two example deployment scenarios in a multi-RATnetwork (LTE and WiFi);

FIG. 7 shows an example of the Layer 2 Structure for the uplink of amulti-RAT network in accordance with the present invention;

FIG. 8 is a flowchart of steps in a method embodying the invention; and

FIG. 9 illustrates a possible format of a joint buffer status reportfrom a UE in one embodiment of the present invention.

DETAILED DESCRIPTION

Before describing preferred embodiments of the present invention, someunderlying principles will first be explained.

Embodiments of the present invention can provide a novel buffer statusreporting scheme which enables the co-ordination of multiple basestations of different RATs (e.g. LTE eNB, UMTS base station, WiFi accesspoint, etc.) with the assistance of the UEs in order to achieveefficient radio resource scheduling for multi-RAT multi-flow aggregationin the uplink. Embodiments of the present invention are principallyaimed at the user plane (data traffic). In practice, it is likely thatcontrol plane traffic is carried over the more capable/more reliable RATamong those available, e.g. LTE.

In this scheme, multiple cells of different RATs can simultaneouslyschedule transport block(s) for transmission from a single UE. (Forsimplicity, it can be assumed that each RAT provides one cell, but itwould be possible for a UE to communicate via more than cellsimultaneously in the same RAT). The conventional approach would be thatfor simultaneous use, different RATs employ different frequencies.However, this does not rule out the possibility that they could use thesame frequencies, for example at different times in the same frame, oreven at the same time.

If the same data is sent via multiple RATs this provides diversity. Ifthe data is different, then this can provide higher data rates. Thedifferent cells can belong to the same base station (where multiple RATsare co-located in the same node as in FIG. 6(B)), or belong to nonco-located base stations of different RATs (FIG. 6(A)). The supportedRATs can be 3GPP radio access technologies, such as GSM, GPRS, UMTS, LTEand beyond; or non-3GPPP radio access technologies, such as WiMAX, CDMA,WiFi, etc.

When a UE is configured with multi-RAT multi-flow aggregation for itson-going application(s), for each of the applications one or severalradio bearers may be allocated with certain QoS requirements.Incidentally, more than one RB may be set up to provide the application:for example, to service a multimedia application one RB for video andanother for audio. Another example is scalable video where a base layeris sent over one RB and enhancement layers over other RB(s) of other,possibly less reliable, RATs; each of these RBs may be supported by oneRAT or multiple RATs. It would also be possible to send multipleversions (with varying levels of redundancy) of a still image or videoclip, over multiple RBs to provide diversity.

On the terminal side, the UE maintains a layer-2 structure, e.g. asshown in FIG. 7. In FIG. 7, the numbered boxes “1”, “2”, “3” representuplink application layer packets. In this example, there are two radiobearers currently allocated to this UE. Especially for RB1, multi-RATmulti-flow aggregation (RAT1 and RAT2 in this example) has beenconfigured. Thus, RB1 is a multi-RAT bearer which spans multiple RATs.RB2, by contrast, is a conventional RB set up in a single RAT.

As illustrated in FIG. 7, a single PDCP Entity is associated with themulti-RAT radio bearer RB1. This PDCP Entity is then associated with twosets of RLC Entities for RAT1 and RAT2 respectively. Note that forsimplicity, it is assumed in this example shown in FIG. 4 both RAT1 andRAT2 use a similar RLC/MAC structure. In practice, it is not necessarilythe case; and different RATs may use their own RLC or “RLC like”structure and MAC layer implementation.

The box labelled “HARQ” in the MAC layer represents the HARQ entitymentioned earlier. As shown, the PDCP Entity and RLC Entity/RLC Entitiesare associated with one radio bearer, while MAC is shared by all radiobearers (both RB1 and RB2 in this example). The HARQ Entity isassociated with one CC in case of CA. There is not necessarily a HARQentity in every RAT (for example, WiFi does not employ HARQ).

Incidentally, “PDCP Entity” is a 3GPP term, which may not have arecognised meaning in other networks (such as WiFi and WiMAX). However,similar functions may be carried out by different entities in othersystems (or perhaps not carried out at all). Thus, non-3GPP RATs mayneed to adopt a simple PDCP function.

Also, although “RLC Entity” is a 3GPP term, there may be similarfunctionality in other non-3GPP networks. For example, the LLC (logicallink control) layer in WiFi systems has similar function although muchsimpler than RLC in 3GPP networks.

FIG. 8 shows steps in a method embodying the invention.

Step S10 is to configure RBs for servicing the UE across multiple RATs.In Step S12, one or more LCIDs is assigned to each RB. That is, when theradio bearer RB1 (with multi-RAT multi-flow aggregation configured) isset up by the network, multiple logical channel IDs are assigned to thisRB that may be associated with different RATs (e.g. as shown in FIG. 7,LC11 and LC12 for RB1). Also, logical channels associated with a certainRAT may be grouped into one logical channel group for radio resourcescheduling purposes. Thus, in embodiments of the present invention thereis no longer a one to one correspondence between RBs and LCs. A singleRB may span multiple RATs and be associated with multiple LCs, whilstLCs of the same RAT may be grouped together to form an LCG.

In step S14, on the terminal side, the UE performs the buffer statusreporting procedure, according to the configuration, on all involvedRATs (depending on the requirements of different RATs) and sendsreports/indications to one or more involved base stations. This isdenoted in FIG. 8 by step S14, “transmit joint BSR with entries for aset of LCIDs”, since the joint BSR is a preferred form of such reportingas explained later.

The buffer status reporting procedure may be triggered by the arrival ofdata for UL transmission in the UE's buffer. If there is no data to betransmitted on the UL, there is no need to send a BSR from the UE'sviewpoint. However, transmission of the BSR may nevertheless berequested by the network (e.g. on a periodic basis).

The UE may indicate its preference for a given RAT by assigning data toone specific LCG (corresponding to the preferred RAT). This “preference”refers primarily to preference for transmission of uplink data, butcould also apply to preference for RATs on which to receive downlinkdata. The UE's preference need not be exclusively, or even partly, basedon signal quality, but could be based on economic considerations: forexample use of WiFi will normally be free whereas usage of LTE may incurcharges.

In addition, the UE may leave such LCG (corresponding to a specific RAT)empty, when the quality of this RAT is below the QoS requirements, thatis to say, when the channel quality on this RAT is so poor that therequired QoS cannot possibly be achieved. The UE is able to assess thison the basis of measurements on reference signals. To measure the ULdirectly, reference signals from the UE can be measured by the networkand the results advised to the UE. On the other hand, if UL/DL channelreciprocity can be assumed (as in Time Division Duplex, TDD operationfor example), or if the UL and DL channel quality are stronglycorrelated, the UL channel quality can be estimated from the referencesymbols on the DL in the case where the UE is able to perform DLmeasurements on all the involved RATs.

Additionally, the network may configure constraints on data assigned toa given LCG, for example that the data should not be transmitted via aparticular RAT. This would enable control signalling to be restricted toLTE, while user data could also be sent via WiFi (which requires noexplicit scheduling on the network side).

In step S16, the joint BSR transmitted by the UE is received by thenetwork, more particularly by each of one or more base stationsinvolved. The BSR may be received directly from the UE by each basestation, or alternatively may be received by at least one of the basestations and forwarded to any remaining base stations. It is noted thatthe same base station may operate according to more than one RAT, as inFIG. 6(B).

In step S18, based on the multi-RAT buffer status reports from the UE aswell as other criteria, e.g. pre-defined rules/policy, on the networkside the decision will be made on whether to grant the UE resources on aparticular RAT, which could then be used for next UL transmission ornext period of UL transmissions. This means that the UE may have toreconsider its decision to assign data for transmission on a specificRAT, if the network does not grant resources on that RAT. Generally thesame RAT will handle the re-transmission if required.

Some features or embodiments of the present invention will now bedescribed by way of example.

In a general unless otherwise stated, the embodiments described here arebased on LTE, in combination with other radio access technologies. Sucha network comprises one or more LTE eNodeBs together with other basestations or access points of other RATs, each controlling more than onecell. Each cell may serve one or more terminals (UEs) which may receiveand decode signals transmitted in that cell. The UEs support LTE and atleast one other RAT, In order to schedule the appropriate use oftransmission resources in time, frequency and spatial domains fortransmission to and from the UEs, the network sends control signallingto the UEs. In LTE, in the uplink direction, uplink buffer statusreports (BSR) are needed for the UEs to provide support for QoS-awarepacket scheduling. The details of BSR are configured by RRC signalling.In this invention the buffer status report includes data which may besent using LTE or another RAT.

Radio Bearer Management

For a UE configured with multi-RAT multi-flow aggregation, when theradio bearer is set up for this UE by the network, multiple logicalchannel IDs are assigned to this RB that are associated with differentRATs. Logical channels associated with a certain RAT may be grouped intoone logical channel group for radio resource scheduling reasons.

As variations of this embodiment, a given LCID or LCG may be associatedwith one or more RATs. For example one LCG can be associated with WiFiand the others with LTE. This would enable some data (e.g. delayinsensitive) to be preferentially sent via WiFi. A similar effect may beachieved if data for a given LCID or LCG is excluded from the BSR. Suchdata could be sent via WiFi as initiated by the UE.

As a further variation, data from a given LCID or LCG may be prohibitedfrom being transmitted on a particular RAT. This approach could be usedto ensure that signalling or data with high QoS requirements is sent viaLTE and not via WiFi. The network nodes may exchange information on theUE configuration, for example to allow correct interpretation of BSRssent via different RATs to different network nodes (for example, BSRseach sent via a given RAT to a base station of that RAT, and relating tothat RAT).

Multi-RAT Buffer Status Reporting

In this embodiment, the UEs that have been configured with multi-RATmulti-flow aggregation report the buffer status information of two ormore of the involved RATs by transmitting a joint BSR covering theinvolved RATs. This needs to be instructed by the network via, forexample, RRC signalling in LTE.

FIG. 9 shows a possible format for such a joint BSR, in which each RATinvolved in the report is identified by an ID field, followed by anindication of the buffer status for that RAT, in other words anindication of the amount of data which the UE wishes to transmit, in thenext transmission time period to which the report applies, via that RAT.Various formats for such a report are possible, as will be appreciatedby those skilled in the art. The format of the report, and time periodto which the report applies, may vary depending on the trigger for thereport (e.g. periodic trigger from the network, or ad-hoc trigger due todata arrival in the buffer).

Thus, different from the existing BSR, this new type of report containsinformation of multiple RATs (both 3GPP RATs and non-3GPP RATs) andneeds to be available to all involved base stations. This can be donethrough individual physical channels of each of the different RATs, orusing only one RAT, and with information transfer between base stations.Alternatively, this can be done using or an UL channel that is availablefor all base stations. Thus, the present invention may provide a jointbuffer status report covering all (or some) involved RATs.

UE may indicate its preference of RAT by assigning data to one specificLCG (corresponding to the preferred RAT). In addition, the UE may leavesuch LCG (corresponding to a specific RAT) empty when the quality ofthis RAT is below the QoS requirements. This can be achieved, forexample, by a zero value of a field corresponding to the RAT concernedin a “joint” BSR. More generally, one or more reserved values may bedefined to denote the UE's preference not to employ a specific RAT forits uplink transmission. Alternatively, the same effect may be achievedby omitting one or more fields in the BSR provided for a specific RAT orLCG.

Various modifications are possible within the scope of the presentinvention.

The above description refers to a UE, but the invention is alsoapplicable to other types of wireless device receiving data on adownlink of a multi-RAT system, for example a relay or picocell basestation. In that case, the relay/picocell behaves as an UE towards abase station that controls the radio resources (a donor eNB in LTEterminology).

Also, although the description assumes that different base stationsemploy different RATs, it would be possible for some of the basestations to be using the same RAT but operated by different mobileoperators (in other words in different RANs using the same RAT). Asexemplified by FIG. 6(B), the same base station may operate inaccordance with more than one RAT simultaneously; in other words it mayprovide “base station means” for more than one RAT.

Reference was made above to associating logical channels with a certainRAT to form an LCG; thus, an LCG would normally apply to one RAT.However it would also be possible for one LCG to span multiple RATs.

More generally, although conventionally a given LCID or LCG is onlyassociated with one RAT, there is no need to follow this restriction inthe present invention. Assuming that the configured characteristics ofan RB are mainly related to the UE's application requirements, then forexample it would be possible to assign an RB to one LC which is thenmapped to two different RATs. Alternatively an RB could be assigned totwo different LCs each of which can be associated with a different RAT.

It is noted that not every RAT will necessarily employ the sametransmission time periods such as frames. The base stations (orhigher-level nodes) of the involved RATs may need to agree a commontiming structure to which the transmission time units of each individualRAT can be mapped. However, different frame lengths at the physicallayer may not be an issue at higher layers, which may not need toconform to a particular frame timing.

To summarise, embodiments of the present invention enable a novel bufferstatus reporting scheme which enables the co-ordination of multiple basestations of different RATs (e.g. LTE eNB, UMTS base station, WiFi accesspoint, etc.) with the assistance of the UEs in order to achieveefficient radio resource scheduling for multi-RAT multi-flow aggregationin uplink.

When a radio bearer (with multi-RAT multi-flow aggregation configured)is set up by the network, multiple logical channel IDs are assigned tothis RB that may be associated with different RATs. Logical channelsassociated with a certain RAT (or a given set of RATs) may be groupedinto one logical channel group for radio resource scheduling purposes.On the terminal side, the UE performs the buffer status reportingprocedure, according to the configuration, on all involved RATs andsends reports/indications to one or more involved base stations.

INDUSTRIAL APPLICABILITY

The invention enables efficient uplink radio resource scheduling formulti-RAT multi-flow aggregation in a mobile communication system whereterminals are configured to transmit and receive data simultaneouslyusing multiple base stations of different radio access technologies(RATs). This invention allows multi-RAT radio resources to be usedsimultaneously to a single UE for uplink transmission thus improvingdata rates and the user experience across the entire coverage area,furthermore improving the overall system load balancing.

The invention claimed is:
 1. A method for uplink communication between aterminal and a multi-RAT (radio access technology) wirelesscommunication network comprising one or more base stations, the methodcomprising: in the multi-RAT wireless communication network, configuringradio bearers, each radio bearer to be carried by one or more radioaccess technologies (RATs) among a plurality of RATs available to theterminal, and associating logical channels with radio bearers byassigning to each radio bearer one or more logical channels; in theterminal, transmitting one or more buffer status reports to a basestation operating according to one or more of the RATs, where at leastone of the buffer status reports contains information on data to be senton a first set of logical channels associated with a first set of radiobearers where the first set of radio bearers is to be carried by morethan one RAT; and in the base station, forwarding at least a relevantpart of the at least one buffer status report to one or more basestations operating according to an other RAT by which the first set ofradio bearers is configured to be carried.
 2. The method according toclaim 1, wherein one or more groups of logical channels are configuredfrom among the first set of logical channels, and the at least one ofthe buffer status reports contains information on data to be sent oneach of the one or more groups of logical channels.
 3. The methodaccording to claim 2, wherein at least one of the one or more groups oflogical channels is configured to contain a second set of logicalchannels associated with a second set of radio bearers where the secondset of radio bearers is to be carried by more than one RAT.
 4. Themethod according to claim 1, further comprising configuring a second setof logical channels associated with a second set of radio bearers to becarried by a single RAT, the method further comprising the terminal,prior to transmitting buffer status reports, assigning data to thesecond set of logical channels for uplink transmission in accordancewith at least one of: a preference for the single RAT; a signal qualitywith respect to the single RAT; a quality of service requirement for thedata; and a network constraint on usage of the single RAT.
 5. The methodaccording to claim 1, further comprising, in the multi-RAT wirelesscommunication network, granting, in respect of a set of logical channelsassociated with a set of said radio bearers, uplink resources on one ormore RATs on a basis of: the one or more buffer status reports; and anetwork policy on usage of each RAT for uplink data transmission.
 6. Themethod according to claim 1, further comprising configuring a second setof logical channels associated with a second set of radio bearers to becarried by one or more of the plurality of RATs available to theterminal excluding a specific RAT.
 7. The method according to claim 1,wherein at least one of the entries in a buffer status report isassociated with a given RAT, and the terminal indicates a preference notto employ a given RAT for its uplink transmission by a zero value for atleast one of said at least one entries in the buffer status report whichis associated with the given RAT.
 8. The method according to claim 1,wherein at least one of the entries in a buffer status report isassociated with a given RAT, and the terminal indicates a preference notto employ the given RAT for its uplink transmission by omitting at leastone of said at least one entries in the buffer status report which isassociated with the given RAT.
 9. A multi-RAT (radio access technology)wireless communication system, comprising: a terminal arranged toperform at least uplink communication via first and second RATs; a firstbase station operating according to the first RAT; and a second basestation operating according to the second RAT; wherein the first andsecond base stations are arranged to co-operate to configure radiobearers to be carried at least on an uplink by one or more of the firstand second RATs, and to associate logical channels with the radiobearers by assigning one or more logical channels to the radio bearer;and the terminal is arranged to assist multi-RAT uplink scheduling bytransmitting one or more buffer status reports where at least one of thebuffer status reports contains information on data to be sent on a setof logical channels associated with a set of said radio bearers to becarried by more than one RAT, wherein the one or more buffer statusreports are transmitted to the first base station operating according tothe first RAT, and the first base station forwards at least a relevantpart of the at least one buffer status report to the second base stationoperating according to the second RAT, by which second RAT the set ofradio bearers is configured to be carried.
 10. A base station operatingaccording to a first RAT (radio access technology) for use in amulti-RAT wireless communication system in which system a terminal isarranged to perform at least uplink communication via first and secondRATs; the base station arranged to: co-operate with a second basestation operating according to the second RAT, to configure radiobearers to be carried at least on an uplink by one or more of the firstand second RATs, and to associate logical channels with the radiobearers by assigning one or more logical channels to the radio bearer;wherein the base station is further arranged to: receive, from theterminal, one or more buffer status reports where at least one of thebuffer status reports contains information on data to be sent on a setof logical channels associated with a set of radio bearers to be carriedby the first and second RATs; and assign, in respect of the set oflogical channels associated with the set of radio bearers, resources foruplink transmission by the terminal in the first RAT, in co-operationwith the second base station assigning resources in the second RAT, on abasis of the at least one of the buffer status reports by forwarding atleast a relevant part of the at least one buffer status report to thesecond base station operating according to the second RAT, by whichsecond RAT the set of radio bearers is configured to be carried.
 11. Aterminal for use in a multi-RAT (radio access technology) wirelesscommunication system in which the terminal is arranged to perform atleast uplink communication via first and second RATs; the terminalarranged to: receive a configuration of radio bearers to be carried atleast on an uplink by one or more of the first and second RATs, in whichconfiguration logical channels are associated with the radio bearers byassigning one or more logical channels to each radio bearer; where theterminal is further arranged to: transmit, to a base station operatingaccording to one or more of the RATs, one or more buffer status reportswhere at least one of the buffer status reports contains information ondata to be sent on a set of logical channels associated with a set ofradio bearers where the set of radio bearers is to be carried by thefirst and second RATs, whereby at least a relevant part of the at leastone buffer status report is forwarded to one or more base stationsoperating according to an other RAT by which the first set of radiobearers is configured to be carried; and receive, in response to thebuffer status reports, an assignment of resources for uplinktransmission by the terminal in the first and second RATs with respectto the set of logical channels.